The application of molecular genetics to syndromes of familial cancer has led to the identification of recessive genes encoding possible tumor suppressing proteins. Elucidation of the function of such proteins will in the long term yield new insights into the pathogenesis and treatment of malignancy. Molecular analysis of the WAGR syndrome, in which children suffer from Wilms' tumors, often bilateral, at a young age, aniridia, genitourinary malformations and mental retardation, led to the molecular cloning of the WT-1 recessive tumor suppressor gene. WT-1 encodes a sequence specific DNA-binding repressor of gene transcription. Loss of repression by WT-1 may predispose to neoplasia and malformations by the deregulation of growth promoting genes. We hypothesize that WT-1 represses transcription through specific inhibitory contacts with components of the transcriptional machinery. Accordingly, we will characterize the mechanism of action of the WT-1 by determining its ability to repress transcription from a defined promoter in-vivo, using procedures similar to those we have used to characterize transcriptional repression by the Drosophila Kruppel protein. We will analyze the transcriptional effects of mutations of the WT-1 protein found in patients with the Denys-Drash syndrome and spontaneous Wilm's tumors, which we speculate to be dominant negative mutations of WT-1. We will reconstitute transcriptional repression by WT-1 in-vitro, in order to determine which phase of transcriptional initiation is blocked by the WT-1 protein. Collectively, these studies will yield insight into the molecular mechanism of a transcription factor whose alteration or deletion can lead to malignancy and malformations.